From 4560e7c3317c7a2b370e36dadd3a3bac2ed70818 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Mon, 28 Oct 2013 12:15:32 +0100 Subject: [PATCH] s390/vtime: correct idle time calculation Use the ACCESS_ONCE macro for both accesses to idle->sequence in the loops to calculate the idle time. If only one access uses the macro, the compiler is free to cache the value for the second access which can cause endless loops. Cc: stable@vger.kernel.org # 3.6+ Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/smp.c | 4 ++-- arch/s390/kernel/vtime.c | 2 +- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index 739313d..dc4a534 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -920,7 +920,7 @@ static ssize_t show_idle_count(struct device *dev, idle_count = ACCESS_ONCE(idle->idle_count); if (ACCESS_ONCE(idle->clock_idle_enter)) idle_count++; - } while ((sequence & 1) || (idle->sequence != sequence)); + } while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence)); return sprintf(buf, "%llu\n", idle_count); } static DEVICE_ATTR(idle_count, 0444, show_idle_count, NULL); @@ -938,7 +938,7 @@ static ssize_t show_idle_time(struct device *dev, idle_time = ACCESS_ONCE(idle->idle_time); idle_enter = ACCESS_ONCE(idle->clock_idle_enter); idle_exit = ACCESS_ONCE(idle->clock_idle_exit); - } while ((sequence & 1) || (idle->sequence != sequence)); + } while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence)); idle_time += idle_enter ? ((idle_exit ? : now) - idle_enter) : 0; return sprintf(buf, "%llu\n", idle_time >> 12); } diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c index e312c48..8c34363 100644 --- a/arch/s390/kernel/vtime.c +++ b/arch/s390/kernel/vtime.c @@ -191,7 +191,7 @@ cputime64_t s390_get_idle_time(int cpu) sequence = ACCESS_ONCE(idle->sequence); idle_enter = ACCESS_ONCE(idle->clock_idle_enter); idle_exit = ACCESS_ONCE(idle->clock_idle_exit); - } while ((sequence & 1) || (idle->sequence != sequence)); + } while ((sequence & 1) || (ACCESS_ONCE(idle->sequence) != sequence)); return idle_enter ? ((idle_exit ?: now) - idle_enter) : 0; } -- 2.7.4